Melanoma is a major world health problem with most deaths occurring due to metastatic spread of the disease. Although genetic basis of melanoma formation has been well established whether metastatic progression of melanoma is driven by genetic or epigenetic events remains unclear. With a hypothesis that epigenetic events may be a key driving force for metastatic progression, we performed an in vivo gain-of-function screen that identified 10 epigenetic regulators as drivers of melanoma metastasis. In this proposal, we focus on one of the top hits - UCHL5 - which is a deubiquitinase and a mammalian specific subunit of Ino80 chromatin remodeling complex. Using in vitro and in vivo validation experiments, we have verified role of UCHL5 in promoting melanoma invasion and metastasis. Importantly, our preliminary studies show that UCHL5 involves its deubiquitinase activity as well as its association with Ino80 in promotion of invasion. In addition, we find that UCHL5 may regulate important pro-metastatic pathways such as RhoA-LIMK-Cofilin and SLIT-ROBO signaling via direct regulation of ARHGAP29 and SLIT2 respectively. Therefore, the objective of this proposal is to examine the contribution of UCHL5 and its regulation of epigenome reprogramming in driving melanoma metastasis. In the first aim, we propose to characterize UCHL5 mediated epigenome reprogramming using human melanoma cultures in conjunction with animal models and cutting- edge epigenomic technologies. We will assess dynamics of nucleosome position and reprogramming of superenhancer elements by UCHL5 and assess contribution of Ino80 as well as YAP1, which we have identified as a novel interactor of UCHL5. In the second aim, we will study signaling events downstream of UCHL5 with a focus on ARHGAP29 mediated regulation of RhoA-LIMK-Cofilin signaling and actin dynamics. In the third aim, we propose to examine therapeutic utility of UCHL5 inhibition alone as well as in combination with current standard-of- care melanoma therapies in pre-clinical transgenic animal models of metastatic melanoma. Together, our proposal will not only provide new insights into the epigenetic mechanisms driving melanoma metastasis but also provide proof-of-concept evidence for use of UCHL5 inhibitors as a therapeutic strategy in metastatic melanoma.